Replace favorites entities with a PreferencesManager, that returns
observables for:
- Module preferences (by module UUID)
- Provider preferences (by ProviderID)
Automate preferences availability in:
- Module views (empty for now)
- VPN server view (favorites)
Synchronize preferences by making this a CloudKit container. Preferences
are also available in the Tunnel by storing the container in the App
Group.
There was duplication and a ugly `#if os(macOS)` with some footers
explicitly rendered on macOS with .themeFooter() (now .themeSubtitle()).
Move this logic to the .themeSection() modifiers by adding a
`forcesFooter` parameter. When true, a fake footer is added on macOS as
the last row of a section.
Davide